System and method for determining forces on a load-bearing tool in a wellbore

ABSTRACT

A system and method for sensing forces on a load-bearing tool located in a wellbore, according to which forces acting on the tool are sensed, and other conditions in the wellbore are measured. The forces on the tool caused by the measured conditions are subtracted from the sensed forces to determine the direct force acting on the tool.

BACKGROUND

This invention relates to a system and method for determining forces on a load-bearing tool in a wellbore in a downhole oil and gas recovery operation system.

An example of a load-bearing tool of the above type is a retrievable packer that is inserted in a wellbore in many oil field applications for the purpose of sealing against the flow of fluid and thus isolate one or more portions of the wellbore for the purposes of treating or producing the well. The packer is suspended from a workstring, or the like, in the wellbore, and includes one or more elastomer elements which are activated, or set, so that the elements are forced against an inner surface of the wellbore, or casing, and compressed to seal against the flow of fluid and therefore to permit isolation of certain zones in the well. The packer can be set by either setting down weight through the workstring which imparts a compressive load to the packer or by picking up on the workstring which imparts a tensile load to the packer. These setting loads or setting forces are referred to as a direct force.

After being set in the above manner, the packer can be subjected to various additional forces such as those related to workstring pressure and/or annulus pressure or by thermal expansion and contraction that occur when various fluids are pumped down the workstring. Since these forces may change the setting force on the packer and may otherwise adversely affect its operation, it is important that these additional forces be measured and their values either stored or transmitted to the surface in real time so as to permit remedial action.

To this end, strain gauges have been used to measure the direct force. However, strain gauges are sensitive to other conditions in the wellbore that can cause the additional forces on the packer. Therefore, the strain gauges measure a total force that is the sum of the direct force and the additional forces instead of measuring only the desired direct force.

In order to correct for this, various forms of mechanical and hydraulic devices have been used in an effort to compensate for the above additional forces caused by the other conditions in the wellbore. However, these compensation systems require additional components that can increase the length, complexity and cost of the system.

Therefore, what is needed is a system that compensates for the above additional forces while requiring few or no additional components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an schematic/elevational view of a downhole tool including an embodiment of a system according to the invention.

FIG. 2 is a partial schematic, enlarged, side view of the embodiment of FIG. 1.

FIG. 3 is a schematic view of the electronics used in the embodiment of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1, the reference numeral 10 refers to a wellbore penetrating a subterranean ground formation F for the purpose of recovering hydrocarbon fluids from the formation F. A load-bearing tool 12 is lowered into the wellbore 10 to a predetermined depth by a workstring 14, which can be in the form of coiled tubing, jointed tubing, drill pipe, or the like, which is connected to the upper end of the tool 12. The tool 12 is shown generally in FIG. 1 and will be described in detail later.

The workstring 14 extends from a rig 16 located above ground and extending over the wellbore 10. The rig 16 is conventional and, as such, includes support structure, a motor driven winch, or the like, and other associated equipment for lowering the tool 12, via the workstring 14, to a predetermined depth in the wellbore 10.

The upper portion of the wellbore 10 can be lined with a casing 20 which is cemented in the wellbore 10 by introducing cement in an annulus formed between the inner surface of the wellbore 10 and the outer surface of the casing 20, all in a conventional manner. A production tubing 22 having a diameter greater than that of the tool 12, but less than that of the casing 20, may also be installed in the wellbore 10 in a conventional manner and extends from the ground surface to a predetermined depth in the casing 20.

As viewed in FIG. 2, the tool 12 has an upper portion 12 a that supports a series of sensing and measuring devices that will be described, and a lower portion that is in the form of a packer 12 b.

When actuated, or set, the tool 12 engages the corresponding inner wall portion of the casing 20 for the purpose of sealing against the passage of fluids across the tool 12.

A series of sensors 34 are mounted to the upper portion 12 a of the tool 12 to sense a direct force. Each sensor 34 can be in the form of a metal foil strain gauge whose resistance varies in response to various forces applied thereto, which forces are largely in the form of tensile and compressive stresses on the tool 12 caused by setting the tool 12. Although only four sensors 34 are shown, it is understood that this number can vary.

As stated above, the sensors 34 are sensitive to other conditions in the wellbore 10 that can cause additional forces to act on the tool 12. Examples of these conditions include the temperature in the wellbore 10, pressure in the workstring 14, and/or differential pressure across the tool 12. To compensate for this a series of pressure gauges 36 and temperature gauges 38 are also mounted to the upper portion 12 a of the tool 12. The gauges 36 and 38 can be in the form of piezo-resistive transducers, or any other conventional design, and, as such, are adapted to measure the pressure and temperature conditions in the wellbore 10 that affect the tool 12, and output corresponding signals. Although only two pressure gauges 36 and two temperature gauges 38 are shown mounted to the tool 12, it is understood that this number can vary. Pressure gauges 36 may for example be located in a cavity in the tool 12 and connected by ports to the interior of the workstring 14 and an annulus formed between the outer surface of the tool 12 and the inner wall portion of the casing 20.

A processor 40 is also mounted to the upper portion 12 a of the tool 12, and, as shown in FIGS. 2 and 3, is electrically connected to the sensors 34 and the gauges 36 and 38. The processor 40 receives the above output signals from the sensors 34 and the gauges 36 and 38 and processes them in a manner to be described.

In operation, the tool 12 is lowered to a predetermined depth in the wellbore 10 via the workstring 14, and the packer 12 b is then set in a conventional manner. In performing this sealing function, the tool 12 is subjected to various forces, described below, in connection with the oil recovery process.

The sensors 34 sense a total force acting on the tool 12 and output corresponding signals to the processor 40. This total force includes the direct force on the tool 12 caused by setting the tool 12. However, the sensors 34 also sense the additional forces caused by other conditions in the wellbore 10 such as forces caused by thermal expansion and contraction that occur when various fluids are pumped down the workstring 14.

In order to determine these additional forces, the gauges 36 and 38 can measure the pressure in the workstring 14, the differential pressure across the tool 12, and/or the temperature in the wellbore 10 around the tool 12 and output corresponding signals to the processor 40.

The processor 40 includes a readable medium, or software, including instructions for execution by the processor 40, for calculating the direct force on the tool 12 from the total force and the additional forces in accordance with well known engineering principles. The additional force components are subtracted from the total force on the tool 12 measured by the sensors 34 to arrive at the direct force on the tool 12. The processor 40 then stores data based on these forces for downloading after the tool 12 is removed from the well, or the processor 40 can be designed to output a corresponding signal that is transmitted to the rig 16 in any conventional manner. This data is collected at the rig 16 and used to determine if the direct force caused by setting the tool 12 is such that remedial action is required.

It is understood that variations may be made in the foregoing without departing from the scope of the invention. Examples of some variations are as follows:

-   -   (1) The number, the particular type, location, and the relative         orientation, of the sensors 34 and the gauges 36 and 38 can be         varied within the scope of the invention.     -   (2) The gauges 36 and 38 are merely examples of measuring         devices that can be used to measure the other conditions in the         wellbore 10 that cause the additional forces on the tool 12, and         therefore other devices can be used.     -   (3) Only one of the gauges 36 and 38 can be used to the         exclusion of the other.     -   (4) The upper portion 12 a of the tool 12 could be eliminated         and the entire tool 12 could be in the form of a packer, in         which case the sensors 34, the gauges 36 and 38, and the         processor 40 would be mounted on the packer.     -   (5) The type of tool to which the sensors 34, the gauges 36 and         38, and the processor 40 are mounted can include any         load-bearing tool or sub connected to the tool that is         insertable in the wellbore 10 in the above manner.     -   (6) A mandrel could be provided that is connected to, or forms         part of, the tool 12 and is adapted to receive the sensors 34,         the gauges 36 and 38, and the processor 40.     -   (7) The tool 12, or other load-bearing tool, can be part of a         tool assembly including other tools (not shown) for performing         other operations in the wellbore 10.     -   (8) The spatial references used above, such as “upward”,         “downward”, “vertical”, “radial”, etc. are for the purpose of         illustration only and do not limit the specific orientation or         location of the structure described above.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents. 

1. A method of determining a direct force acting on a load-bearing tool connected to a workstring, comprising the steps of: sensing a total force acting on the tool when located in a wellbore, wherein the total force comprises the direct force acting on the tool and additional forces acting on the tool; measuring at least one condition in the wellbore that causes the additional forces; calculating the additional forces from the measured condition; and subtracting the additional forces from the sensed total force to determine the direct force acting on the tool.
 2. The method of claim 1 wherein the measured condition is the temperature in the wellbore around the tool.
 3. The method of claim 1 wherein the measured condition is the differential pressure across the tool.
 4. The method of claim 1 wherein the measured condition is the pressure in the workstring.
 5. The method of claim 1 wherein the steps of calculating and subtracting are done by a processor that receives signals corresponding to the sensed total force and measured conditions.
 6. The method of claim 1 wherein the direct force is a tensile or compressive stress on the tool.
 7. The method of claim 1 wherein the tool comprises a packer, and the direct force is a force used to set the packer.
 8. A system for determining a direct force acting on a load-bearing tool connected to a workstring, comprising: at least one sensor for sensing a total force acting on the tool when located in a wellbore, wherein the total force comprises the direct force acting on the tool and additional forces acting on the tool; at least one gauge for measuring at least one condition in the wellbore that causes additional forces on the tool; and a processor for calculating the additional forces on the tool resulting from the measured conditions, and subtracting the additional forces from the sensed total force to determine the direct force.
 9. The system of claim 8 wherein the measured conditions include the temperature in the wellbore around the tool.
 10. The system of claim 8 wherein the measured conditions include the differential pressure across the tool.
 11. The system of claim 8 wherein the measured conditions include the pressure in the workstring.
 12. The system of claim 8 wherein the processor receives signals corresponding to the sensed total force and measured conditions.
 13. The system of claim 8 wherein the direct force is a tensile or compressive stress on the tool.
 14. The system of claim 8 wherein the tool comprises a packer, and the direct force is a force used to set the packer.
 15. A processor readable medium comprising a plurality of instructions for execution by at least one processor, wherein the instructions are for: receiving an input corresponding to a total force acting on a tool when located in a wellbore, wherein the total force comprises a direct force acting on the tool and additional forces acting on the tool; receiving an input corresponding to at least one measured condition in the wellbore that causes the additional forces on the tool; calculating the additional forces resulting from the measured condition; and subtracting the additional forces from the total force to determine the direct force acting on the tool.
 16. The medium of claim 15 wherein the measured condition is the temperature in the wellbore around the tool.
 17. The medium of claim 15 wherein the measured condition is the differential pressure across the tool.
 18. The medium of claim 15 wherein the measured conditions include the pressure in a workstring connected to the tool.
 19. The medium of claim 15 wherein the direct force is a tensile or compressive stress on the tool.
 20. The medium of claim 15 wherein the tool comprises a packer, and the direct force is a force used to set the packer.
 21. A system of determining a direct force acting on a load-bearing tool connected to a workstring, comprising: means for sensing a total force acting on the tool when located in a wellbore, wherein the total force comprises the direct force acting on the tool and additional forces acting on the tool; means for measuring at least one condition in the wellbore that causes the additional forces; and means for calculating the additional forces resulting from the measured condition and subtracting the additional forces from the total force to determine the direct force.
 22. The system of claim 21 wherein the measured condition is the temperature in the wellbore around the tool.
 23. The system of claim 21 wherein the measured condition is the differential pressure across the tool.
 24. The system of claim 21 wherein the measured condition is the pressure in the workstring.
 25. The system of claim 21 wherein the means for calculating and subtracting is a processor that receives signals corresponding to the total force and measured conditions.
 26. The system of claim 21 wherein the direct force is a tensile or compressive stress on the tool.
 27. The system of claim 21 wherein the tool comprises a packer, and the direct force is a force used to set the packer. 